The present invention relates to cutting tools used to cut through soft ground or through relatively soft material that has been laid on the ground, such as asphalt roadways.
Mining, excavating, and road resurfacing operations are typically performed by forcing rotary cutting bits through the material being cut. The cutting bits are mounted on a driven support, such as a rotary drum, fixed beam, or the like to be forced through the material. A typical cutting bit disclosed for example in U.S. Pat. No. 6,113,195 and shown as cutting bit 1 in FIG. 1 herein, comprises a hard carbide tip 2 that is brazed to the front surface of a steel shank 3. The shank is to be mounted in a holder (not shown) by means of a retainer sleeve 4 which permits the bit to rotate freely relative to the holder about the bit""s center axis, while being restrained against axial dislodgment from the holder. Due to being freely rotatable, the tip is basically self-sharpening.
It should be understood that cutting mechanisms of the type described above have been used to cut through hard materials, such as rock and ice, in addition to cutting through softer materials such as asphalt. During the cutting of rock, the highest rate of bit wear occurs at the carbide tip, so the wear life of the bit is determined by the carbide tip. However, during the cutting of relatively softer material, such as asphalt, the highest rate of wear occurs at the shank, i.e., erosion caused by cut asphalt rubbing and impacting against the shank. Thus, when cutting asphalt during a road resurfacing operation, the wear life of the cutting bit is determined by the shank.
It would be desirable to provide a cutting bit that has an increased wear life when used for cutting softer materials such as asphalt.
Disclosed in U.S. Pat. No. 4,725,098 is a cutting bit in which a groove is machined in a tapering side surface of the bit head closely behind a carbide tip mounted in the bit head. Hardfacing is deposited into the groove to form an erosion-resistant annular ring which can be flush with, or project slightly radially beyond, the side surface. Despite being formed of hard material, the ring will be subjected to considerable erosion by cuttings and thus will have a somewhat limited life.
It would be desirable to provide a cutting bit with an erosion-resistant structure which has an enhanced life.
The present invention relates to a cutting bit which comprises a body that includes a shank and a head disposed at a front end of the shank. The head includes a forwardly facing front surface, and a tapered side surface having a cross section which increases in a rearward direction. The bit also includes a cutting tip attached to the front surface of the head and formed of a harder material than the body. The head includes a ledge projecting from the tapering side surface in a laterally outward direction relative to a longitudinal axis of the body. The ledge projects from the tapered side surface at a location spaced rearwardly from a rearwardmost end of the tip, and is oriented substantially perpendicularly to the longitudinal axis.
Preferably, the ledge is oriented such that a laterally outer end of the ledge is situated no farther rearwardly than a laterally inner end thereof. Most preferably, the outer end of the ledge is situated slightly forwardly of the inner end of the ledge, e.g., by inclining the ledge slightly forwardly.
The ledge can be formed integrally of one-piece construction with the rest of the bit body, or can comprise a separate split ring which is elastically held on the body.
The ledge preferably has sufficient width to facilitate the adherence thereto of material, such as asphalt, during an asphalt-cutting operation. For example, the ledge could project laterally outwardly by a distance greater than 10%, most preferably greater than 15%, of a radius of the tapered surface as measured at the point of intersection of the tapered surface with the ledge.